High voltage MOSFET diode reverse recovery by minimizing P-body charges

ABSTRACT

This invention discloses a method for manufacturing a semiconductor power device in a semiconductor substrate comprises an active cell area and a termination area. The method comprises the steps of a) growing and patterning a field oxide layer in the termination area and also in the active cell area on a top surface of the semiconductor substrate b) depositing and patterning a polysilicon layer on the top surface of the semiconductor substrate at a gap distance away from the field oxide layer; c) performing a blank body dopant implant to form body dopant regions in the semiconductor substrate substantially aligned with the gap area followed by diffusing the body dopant regions into body regions in the semiconductor substrate; d) implanting high concentration body-dopant regions encompassed in and having a higher dopant concentration than the body regions e) applying a source mask to implant source regions having a conductivity opposite to the body region with the source regions encompassed in the body regions and surrounded by the high concentration body-dopant regions; and f) etching contact trenches into the source, body contact, and body regions.

This Patent Application is a Divisional Application and claims thePriority Date of a co-pending application Ser. No. 12/587,054 filed onSep. 30, 2009 by common inventors of this Application. The disclosuresmade in the application Ser. No. 12/587,054 are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the configurations and methods ofmanufacturing semiconductor power devices. More particularly, thisinvention relates to a device configuration and method of manufacturingsemiconductor power devices integrated with Schottky diode withoutrequiring additional masks, for reducing the turn off time and the powerlosses.

2. Description of the Prior Art

There is a great demand for implementing a semiconductor power device byintegrating the Schottky diode as an internal diode. Specifically, thehigh voltage metal oxide semiconductor field effect transistor (HVMOSFET) behaves like a P-i-N diode with a negative drain-to-sourcevoltage Vds<0, due to the built-in body diode formed by the P+, P− Body,and N-epi as shown in FIG. 1A. A high level injection into the N-Epiregion from the P−body regions causes a large turn off time and losses.Furthermore, a high rate of current variation, i.e., a large di/dt,causes a voltage spike and reduces a “softness factor” S. However, inorder to improve the performance of the HV MOSFET, there is a need toreduce the turn off time and losses, i.e., to reduce the reverserecovery charge (Qrr), recovery tune (Trr), and to increase the softnessfactor S. A HV MOSFET when integrated with an internal Schottky diodeimproves the performance of the HV MOSFET by resolving these technicallimitations.

In addition in the above-mentioned demand for implementing thesemiconductor power device with an integrated Schottky diode, thesemiconductor power devices are widely implemented in a power supply andmotor control applications. The semiconductor power devices are oftenformed with a full bridge type of topology as shown in FIG. 1B. For thistype of application, an internal diode is very advantageous to functionas a free-wheeling diode. A high voltage MOSFET, a super-junctionsemiconductor power device, and IGBT devices when implemented for thepower supply and motor control applications often suffer from thelimitations of high Qrr and power loss. A semiconductor power devicewhen integrating the Schottky diode as an internal diode can resolvethese technical problems. However, conventional configurations andmethods of manufacturing the semiconductor power devices usually requirean additional mask to block an area in order to integrate the Schottkydiode as an internal diode of the power device in that area. Productioncosts are adversely affected due to additional this mask requirement.

For all these reasons, them are great and urgent demands to improve theconfigurations and method of manufacturing the semiconductor powerdevice to integrate with the Schottky diodes as an internal diode and toimprove the Qrr, Trr and S such that the above-discussed technicallimitations and difficulties can be resolved.

SUMMARY OF THE PRESENT INVENTION

It is therefore an aspect of the present invention to provide a new andimproved method and device configuration to manufacture a semiconductorpower device to integrate with a Schottky diode without requiring anadditional mask.

Specifically, it is an aspect of the present invention to provideimproved device configuration and method for manufacturing asemiconductor power device to integrate with Schottky diodes withoutadditional mask while significantly reducing the Qrr, Trr and increasingthe softness factor S.

It is another aspect of the present invention to provide improved deviceconfiguration and method for manufacturing a semiconductor power deviceto integrate with Schottky diodes by reducing the distance between theedge of the planar gates to the field oxide to form the self-alignedbody regions and to covering the top surfaces over the source and bodyregions with a Schottky metal to function as a source and emitter metalto integrate the Schottky diode directly as part of the transistor cellswithout increasing the cell pitch such that significantly reduces theQrr by about 50%, Trr by 20% and increases the softness factor S byabout 33%.

It is another aspect of the present invention to provide improved deviceconfiguration and method for manufacturing a semiconductor power devicewith reduced amounts of body-type charges available for high levelinjection to reduce the Qrr, Trr and increasing the softness factor S.

Briefly in a preferred embodiment this invention discloses asemiconductor power device disposed in a semiconductor substrate. Thesemiconductor power device comprises an active cell area and atermination area. The semiconductor power device further comprises agate comprises a patterned polysilicon layer disposed on a top surfaceof the semiconductor substrate. The semiconductor power device furthercomprises a patterned field oxide layer disposed in the termination areaand also in the active cell area at a gap area away from the patternedpolysilicon layer on the top surface of the semiconductor substrate. Thesemiconductor power device further comprises doped body regions disposedin the semiconductor substrate substantially diffused from a regionaligned with the gap area below the top surface and extended to regionsbelow the patterned polysilicon layer and the patterned field oxidelayer. The semiconductor power device further comprises doped sourceregions encompassed in and having an opposite conductivity type from thebody regions. The semiconductor power device further comprises highconcentration body-dopant regions encompassed in and having a higherdopant concentration than the body region surrounding the sourceregions. In another embodiment, the semiconductor power device furthercomprises a patterned Schottky metal layer covering an area previouslyoccupied by the field oxide layer in the active cell area andsubsequently removed from on the top surface of the semiconductorsubstrate wherein the patterned Schottky metal layer further extendspartially into the gap area for contacting the body regions and thesource regions to form integrated Schottky diodes for the semiconductorpower device in the active cell area. In another embodiment, thesemiconductor power device further comprises shallow body-dopantimplantations disposed adjacent to the body regions immediately underthe Schottky metal layer. In another embodiment a contact trench isetched into the semiconductor substrate to allow lateral contact to thesource and body contact regions and to reduce the amount of P bodycharges available for high level injections. In another embodiment, thesemiconductor substrate comprises as N-type epitaxial layer forsupporting the body-dopant regions of P-type conductivity encompassingthe source regions N-type conductivity therein. In another embodiment,the semiconductor substrate comprises a P-type epitaxial layer forsupporting the body-dopant regions of N-type conductivity encompassingthe source regions of P-type conductivity therein. In anotherembodiment, the semiconductor power device further comprises a MOSFETpower device. In another embodiment, the semiconductor power devicefurther comprises a N-channel MOSFET power device supported on at N-typesemiconductor substrate. In another embodiment, the semiconductor powerdevice further comprises a P-channel MOSFET power device supported on aP-type semiconductor substrate. In another embodiment, the semiconductorpower device further comprises an insulated gate bipolar transistor(IGBT) power device. In another embodiment, the semiconductor powerdevice further comprises an insulated gate bipolar transistor (IGBT)power device supported on a N-type epitaxial layer including a P-typebottom layer with N-type dopant regions disposed near a bottom surfaceof the semiconductor substrate. In another embodiment, the semiconductorpower device further comprises a superjunction semiconductor powerdevice comprises alternating charge balanced N-type and P-type dopantcolumns in the semiconductor substrate below the body-dopant regions. Inanother embodiment, the semiconductor power device further comprises asuperjunction semiconductor power device disposed in a N-typesemiconductor substrate comprises P-type columns underneath the bodydopant regions doped with a P-type dopant and N-type columns between theP-type columns.

This invention further discloses a method for manufacturing asemiconductor power device in a semiconductor substrate comprises anactive cell area and a termination area. The method comprises steps ofA) growing and patterning a field oxide layer in the termination areaand also in the active cell area on a top surface of the semiconductorsubstrate; B) depositing and patterning a polysilicon layer on the topsurface of the semiconductor substrate at a gap distance away from thefield oxide layer; and C) performing a blank body dopant implant to formbody dopant regions in the semiconductor substrate substantially alignedwith the gap area followed by diffusing the body dopant regions intobody regions in the semiconductor substrate. In another embodiment, themethod further includes a step of implanting high concentrationbody-dopant regions encompassed in and having a higher dopantconcentration than the body regions and applying a source mask toimplant source regions having a conductivity opposite to the body regionwith the source regions encompassed in the body regions and surroundedby the high concentration body-dopant regions. In another embodiment,the method further includes a step of depositing an insulation layer ontop of semiconductor power device and applying a contact mask to opencontact openings and remove the field oxide and etch contact trenches inthe semiconductor substrate: and depositing a metal layer filling in thecontact openings to contact the body regions and the source regions. Inanother embodiment, the method further includes a step of depositing aninsulation layer on top of the semiconductor power device and applying acontact mask to open contact openings and remove the field oxide; andimplanting a shallow body-dopants adjacent to the body regionsimmediately below the contact trench. In another embodiment, the step ofmanufacturing the semiconductor power device further comprises a step ofmanufacturing a MOSFET power device. In another embodiment, the step ofmanufacturing the semiconductor power device further comprises a step ofmanufacturing an IGBT power device. In another embodiment, the step ofmanufacturing the semiconductor power device further comprises a step ofmanufacturing an IGBT power device in a N-type semiconductor substrateand implanting a P-type bottom layer with N-type dopant regions near abottom surface of the semiconductor substrate. In another embodiment,the step of manufacturing the semiconductor power device furthercomprises a step of manufacturing a superjunction semiconductor powerdevice by forming in the semiconductor substrate alternating N-type andP-type dopant columns in the semiconductor substrate below thebody-dopant regions.

These and other objects and advantages of the present invention will nodoubt become obvious to those of ordinary skill in the art after havingread the following detailed description of the preferred embodiment,which is illustrated in the various drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross sectional view for showing the conventional planar HVMOSFET devices without integrated Schottky diode.

FIG. 1B shows a configuration of a full bridge circuit implemented in apower supply and motor control device

FIG. 2 is a cross sectional view of a HVMOSFET device with an integratedSchottky diode of this invention.

FIG. 2-1 is a cross sectional view to show the termination structure ofthe high voltage MOSFET (HV MOSFET) semiconductor power device of thisinvention.

FIGS. 3A to 3F are a series of cross sectional views for showing theprocessing steps to manufacture a HV MOSFET device of this invention.

FIGS. 3A-1 to 3F-1 are a series of corresponding cross sectional viewsin termination area for each of the processing steps of FIGS. 3A to 3F.

FIG. 4 is a cross sectional view of an insulated gate bipolar transistor(IGBT) device with an integrated Schottky diode of this invention.

FIGS. 5A and 5B are cross sectional views of two super-junctionsemiconductor power devices of this invention.

FIGS. 6A to 6I are serial cross sectional views for describing themanufacturing processes to fabricate a super-junction semiconductorpower device of FIG. 5A.

FIG. 6D-1, an anneal process is carried out to diffuse the boronimplanted regions to form multiple P−doped columns and FIG. 6D-2 shows asubsection of the figure from FIG. 6D-1 to show the remainder of thesteps.

FIGS. 7A to 7E are serial cross sectional views for describing themanufacturing processes to fabricate another super-junctionsemiconductor power device of this invention.

FIG. 8 is a cross sectional view for showing an alternate super-junctionsemiconductor power device of this invention.

FIGS. 9A and 9B are cross sectional views of power semiconductor devicesillustrating further aspects of this invention.

FIGS. 10A and 10B are top views showing possible layouts forsemiconductor power devices of this invention.

DETAILED DESCRIPTION OF THE METHOD

Referring to FIG. 2 for a cross sectional view of active cell 100 of ahigh voltage MOSFET (HV MOSFET) semiconductor power device of thisinvention. The HV MOSFET device is supported on an N+ silicon substrate105 with an epitaxial layer 110 formed on top of the N+ substrate 105. Aplanar gate 125 is formed on top of a gate oxide layer 120. A P−bodyregion 130 is formed in the epitaxial layer below the gate oxide layer120 encompassing an N+ source region 135. The MOSFET device 100 furtherincludes a P+ doped region 140 within the P−body region 130. A sourcemetal 150 covering the top surface with direct contact to the sourceregion 135 and the P−body region 130. A drain metal 160 to function as adrain electrode is formed on the back side of the semiconductorsubstrate 105 thus forming an active cell of vertical MOSFET powerdevice. The drawing is not to scale, as the substrate 105 is typicallyseveral times thicker than the epitaxial layer 110. A contact trench 142is formed to make side contact to the source region 135 and the P+ bodycontact region 140. The contact trench can help reduce the cell pitch ofactive cell 100, and also reduce the amount of body type chargesavailable for high level injection. This improves the reverse recoverycharacteristics, Qrr, Trr, and S, while also improving the Rdson becauseof the smaller cell pitch. The MOSFET device may be integrated with aninternal Schottky diode by applying a Schottky metal as the or under thesource metal 150, contacting the source region 135, the P+ region 140and the P−body region 130 and a Schottky region 145 adjacent to theP−body region 130. An ultra shallow P implantation layer 145 may beformed immediately underneath the Schottky metal 150 in the Schottkyregion to adjust the Schottky barrier height and reduce a leakagecurrent. A high voltage MOSFET (HV MOSFET) semiconductor power devicemay include a plurality of active cells 100 connected in parallel toimprove current handling capability. The high voltage MOSFET (HV MOSFET)semiconductor power device further includes a termination structuresurrounding the active cells in the periphery area in order to withstandthe voltage near the die edge. FIG. 2-1 shows the termination structureof the high voltage MOSFET (HV MOSFET) semiconductor power device thatis integrated with a Schottky diode of this invention. The terminationstructure includes a plurality of field plates 125′ electricallyconnected to floating guard rings 130′ by metal conductor 150′ throughguard ring contact implants 140′ and extending over field oxides 115′beyond the lateral boundary of guard ring 130′. Termination trenches142′ may be formed as a side-result of forming the contact trenches 142,but do not affect the operation of the termination structure.

FIGS. 3A to 3F are a series of cross sectional views for illustratingthe processing steps for manufacturing a high voltage MOSFET (HV-MOSFET)100 shown in FIG. 2 and FIGS. 3A-1 to 3F-1 are the corresponding crosssectional views in termination area in each processing step for forminga termination area similar to the one shown in FIG. 2-1. A high voltagedevice requires termination structures in order to withstand the voltagenear the die edge. In FIGS. 3A and 3A-1, the process starts with an Nbuffer doping substrate 105 supporting an N-epitaxial layer 110 with alayer thickness of about 50 to 75 micrometers grown thereon. In FIGS. 3Band 3B-1, a field oxide layer is grown and etched by applying a firstmask (not shown) to form field oxide 115 in active area and 115′ intermination area. In FIG. 3C, a gate oxide layer 120 is grown followedby depositing as polysilicon layer 125 on top of the gate oxide layer120 and then patterning the polysilicon layer into the gate 125 byapplying a second mask not specifically shown). Thin oxide layer 120′and polysilicon structure 125′ are formed in the same process in thetermination area as shown in FIG. 3C-1. In FIG. 3D, a P−body dopantimplant is carried out followed by a diffusion process to form theP−body region 130. A third mask (not shown) is applied to carry out anN+ source implant to form the source region 135. A P+ implant is alsoperformed after the removal of source implant mask to form a P+ bodycontact region 140 below and possibly besides the N+ source region 135.The P−body dopant implant and the P+ implant use the existing fieldoxide and the gate poly 125 as a mask, and so need no additional mask.The N+ implant is at a much higher dosage than the P+ and P−bodyimplants and will dominate in the regions where it is implanted. In thetermination area FIG. 3D-1 source implant is blocked by the third masktherefore only P−body implant and P+ implant are carried out using theexisting field oxide and the gate poly 125 as implant mask to formfloating guard rings 130′ and guard ring contacts 140′. In FIG. 3E, alow temperature oxide (LTO) deposition is carried out to form an oxidelayer 128 followed by applying a fourth mask (not shown) to open acontact opening through the oxide layer 128, and then etching into thesilicon to form contact trench 142, then performing a shallow P− implantto form the shallow P− region 145. While the field, oxide 115 in activearea is removed during contact hole opening process field oxides 115′ intermination area of FIG. 3E-1 remain while opening the contact holesthrough oxide layer 128′ and thin oxide layer 120′ as shown. The contactholes are further etched to form termination trenches 142′. In FIG. 3F,a top metal layer 150 is formed and patterned as a source metal layer byapplying a fifth mask (not shown). A sixth mask (not shown) may beapplied optionally to form and pattern a passivation layer (not shown)and a seventh mask (not shown) to form and pattern a polyimide layer(not shown) over the top surface of the device. A back sidemetallization process is then carried out (also in FIG. 3F) to form thedrain electrode 160 on the back side of the substrate 105. Intermination area metal layer is also patterned into metal conductors150′ to electrically connect polysilicon field plates 125′ to floatingguard rings 130′ therefore forming a plurality of held plates 125′.Field plates 125′ and floating guard rings 130′ form the termination ofdevice in FIG. 3I-1 to sustain high voltage in the edge area. As shownin the above process, the first mask provides both oxides in active areato block body implantation for Schottky formation and in terminationarea for field plate structure termination therefore a dedicated maskfor Schottky formation is not necessary.

FIG. 4 shows a cross-sectional view of an insulated gate bipolartransistor (IGBT) 200 of this invention. The IGBT 200 is formed in asemiconductor substrate 205 that has a first conductivity type, e.g., aP type substrate 205. An epitaxial layer 210 of a second conductivitytype, e.g., an N-epitaxial (epi) layer 210, is supported on top of the Ptype substrate 205. The IGBT 200 is a vertical IGBT device with acollector electrode 260 disposed on a bottom surface of the substrateand an emitter electrode 250 disposed on a top surface and in a contacttrench 242. A gate 225 is supported on top of a gate insulation layer220. An N+ emitter/source region 235 is formed next to the emitterelectrode 250 encompassed in a P−body region 230 extended below theemitter N-region 235 to a region underneath the gate insulation layer220. The IGBT device 200 further includes a N-region doped region 240within the P−body region 230 immediately next to the emitter N-region235. When a gate voltage exceeding a threshold voltage is applied, theinternal PNP bipolar transistor is turned on. An electrical current isconducted from the emitter region 235 through the P body region (in ann-channel) into the N-epi region 210, which induces a the PNP bipolartransistor to turn on thus producing a current from the P+ doped region240 and the P body region 230 to the drift region as part of theN-epitaxial layer 110 to the substrate 205 and then to the collectorelectrode 260. The IGBT device 200 may be further integrated with aninternal Schottky diode by applying a Schottky metal 250 as the emittermetal covering the top surface over and next to the N+ emitter region235, the P+ region 240 and the P−body region 230. The Schottky metal 250is in direct contact with the epitaxial layer 210 and the emitter region235. An ultra shallow P implantation layer 245 is formed immediatelyunderneath the Schottky metal 250 to reduce a leakage current. An N+doped region 205-N is formed in a portion of the P+ substrate layer 205.The N+ doped region 205-N connects the collector electrode 260 to theN-Epi and allows the integrated Schottky diode to be connected betweenemitter electrode 250 and collector electrode 260.

The processing steps for manufacturing the IGBT device are the same asthat described in FIGS. 3A to 3F, except that the starting material is aP substrate 205 supporting an N-epi 210, rather than N+ substrate 105supporting an N-epi 110, and also a N+ implant is performed before backmetallization to form the N+ doped region 205-N. An alternate processmay begin with an N− substrate without an epitaxial layer. Before thebackside metal process as shown in FIG. 3F and after a backside grindingis performed, a P+ blanket implanted at the backside, and a N+ maskedimplant (not shown) is followed to form the N+ substrate region 205-N.The IGBT device 200 integrated with a Schottky diode of this inventionmay also include the termination structure shown in FIG. 2-1 thereforeno additional mask is required for the formation of integrated Schottky.

FIG. 5A shows a cross sectional view of a super-junction semiconductorpower device 300. The super-junction device 200 is supported on an N+silicon substrate 305 with an epitaxial layer 310 with P−doped verticalcolumns 315 in the epitaxial layer formed through multiple epitaxiallayer growth and implantation processes as described below. A planargate 330 is formed on top of a gate oxide layer 325. A P−body region 335is formed in the epitaxial layer below the gate oxide layer 325encompassing an N+ source region 340. An additional P+ body contactregion 336 is formed within the P−body region 335. The P−body regions335 are formed over the P−dopant columns 315 as well as a P+ bodycontact region 336 within the P−body regions 335 immediately below thesource region 340. A source metal 360 covering the top surface andcontact trench 342 with direct contact to the source region 340 and theP+ body contact region 336A drain metal 370 to function as a drainelectrode is formed on the back side of the semiconductor substrate 305thus forming a vertical super-junction power device. The super-junctiondevice may optionally be integrated with an internal Schottky diode byetching a Schottky trench 343 between the gates 330 and applying aSchottky metal 360 as the source metal covering the source region 340,the P+ region 336 and a Schottky contact P−dopant implant 350. The ultrashallow P implantation 350 is formed immediately underneath the Schottkymetal 360 between the gates 330 to reduce a leakage current. Thesuper-junction semiconductor power device 300 of this invention may alsoinclude the termination structure shown in FIG. 2-1 therefore noadditional mask is required. The optional Schottky embodiment is shownin FIG. 5B.

FIG. 5B is a cross sectional view of another super-junctionsemiconductor power device 300′ that has a similar structural featuresof FIG. 5A. The only difference are that the P-draped columns 315′extend to a depth in the epitaxial layer 310 at a distance above thebottom the epitaxial layer 310 interfacing with the bottom substrate N+layer 305, whereas in the power device 300 of FIG. 5A, the P−dopedcolumns 315 extend all the way to the bottom of the epitaxial layer 310,and also that FIG. 5B has the optional Schottky structure as describedabove. The super-junction semiconductor power device 300′ integratedwith a Schottky diode of this invention may also include the terminationstructure shown in FIG. 2-1 therefore no additional mask is required forthe formation of integrated Schottky.

FIGS. 6A to 6J are a series of cross sectional views for illustratingthe processing steps for manufacturing a super-junction semiconductorpower device to reduce the Qrr as that shown in FIG. 5A. In FIG. 6A, theprocess starts with growing a first N-epitaxial layer 310-1 on an N+substrate 305. In FIG. 6B, a mask (not shown) is applied to form thealign-mark followed by growing a pad oxide layer 308. Then a mask 309 isapplied to etch the oxide and carry out a boron implant at 200 KeV toform the P− regions 315-1 in the first epitaxial layer 310-1. The mask309 is removed followed by an anneal process at 900° Celsius for 30minutes to repair the implantation damages. The oxide pad 308 is removedfollowed by growing a second epitaxial layer 310-2 to repeat the aboveprocessing steps to form the second set of P− regions 315-2 in thesecond epitaxial layer 310-2. The same steps are repeated to formmultiple epitaxial layers 310-1 to 310-1K implanted with 315-1 to 315-Kin each epitaxial layer, as shown in FIG. 6C. In FIG. 6D, an annealprocess is carried out at 1150° Celsius for 400-600 minutes to diffusethe boron implanted regions to form multiple P−doped columns 315.

In FIG. 6D-1, an anneal process is carried out at 1150° Celsius for400-600 minutes to diffuse the boron implanted regions to form multipleP−doped columns 315. In order to make P−doped columns that do not extendfully to the N+ substrate 305, as shown in FIG. 5B, the firstN-epitaxial layer 310-1 would not receive the boron implantation 315-1before growing second N-epitaxial layer 310-2. FIG. 6D-2 shows asubsection of the figure from FIG. 6D-1, from which the remainder of thesteps of this process is demonstrated. For simplicity, in these steps,the multiple N-epitaxial layers 310-1 to 310-K are illustrated as asingle continuous N-epitaxial layer 310.

In FIG. 6E, a field oxide layer 320 is grown and etched by applying afirst mask (not shown). In FIG. 6F, a gate oxide layer 325 is grownfollowed by depositing a polysilicon layer 330 on top of the gate oxidelayer 325 and field oxide 320 and then patterning the polysilicon layerinto the gate 330 by applying a second mask (not specifically shown). InFIG. 6G, P dopant implants are carried out to form the P+ body regions336 and P−body regions 335. A source mask as a third mask is applied tocarry out an N+ source implant out to form the source region 340. InFIG. 6H, a BPSG insulation layer deposition is carried out followed byapplying as fourth mask (not shown) to carry out a contact openingprocess to forth the insulation layer 345 with contact openings followedby etching the silicon further to form contact trenches 342. Optionally,as opening may also be etched between the polysilicon gates 330 followedby performing a Schottky implant to form the P−dopant Schottky contactregions 350 between the gates 330 to form a structure like that shown inFIG. 5B. In FIG. 6I, a source metal layer 350 which may also function asa source metal is formed and patterned on the top surface using a fifthmask, and a backside metal 360 is formed on the bottom surface tofunction as a drain electrode. Termination structure as shown in FIG.2-1 is formed at the same process as illustrated in FIGS. 3A-1 to 3F-1.

FIGS. 7A to 7E are a series of cross sectional views for illustrating analternate set of processing steps for manufacturing a super-junctionsemiconductor power device. These steps show an alternate way of formingthe P-columns 315. In FIG. 7A, the process starts with growing anN-epitaxial layer 410 on an N+ substrate 405. In FIG. 7B, a mask 411 isapplied to open a plurality of deep trenches 415 in the epitaxial layer410. In FIG. 7C, the deep trenches are filled with P−doped material415-P, e.g., by epitaxial growth, then in FIG. 7D, a planarizationprocess, e.g. by applying a chemical-mechanical planarization (CMP)process, is performed to remove the P−doped material from the topsurface above the epitaxial layer 410. A plurality of P and N columns415-P and 410-N are therefore formed in the epitaxial layer 410.

In FIG. 7E, the same processes as that described in FIGS. 6E to 6I areperformed to form a super-junction semiconductor power device 400. Thesuper-junction device 400 is supported on an N+ silicon substrate 405with an N-epitaxial layer 410 with P−doped vertical columns 415-P in theepitaxial layer formed on top of the N+ substrate 405, e.g., an arsenide&pant substrate layer in an embodiment as shown. A planar gate 430 isformed on top of a gate oxide layer 425. A P−body region 435 is formedin the epitaxial layer below the gate oxide layer 425 encompassing an N+source region 440. For a high voltage application, the P−body regions435 is formed above the P−dopant columns 415-P. The P+ region 436 isformed within the P−body 435 immediately next to the source region 440.A source metal 460 covering the top surface with direct contact to thesource region 440 and the P−body region 435. A drain metal 470 tofunction as a drain electrode is formed on the back side of thesemiconductor substrate 405 thus forming a vertical super-junction powerdevice. The super-junction device may also be integrated with aninternal Schottky diode by applying a Schottky metal 460 as the sourcemetal covering the top surface over the source region 440, the P+ region436 and a Schottky contact P−dopant implant region 450, and by etching acontact opening between the gates 430. The ultra shallow P implantationlayer 450 is formed underneath the Schottky metal 460 between the gates430 to reduce a leakage current. Termination structure as shown in FIG.2-1 is formed at the same process as illustrated in FIGS. 3A-1 to 3F-1.

FIG. 8 is a cross sectional view &another super-junction semiconductorpower device 400′ that has a similar structural features of FIG. 7E. Theonly difference is the P−doped columns 415-P′ extend to a depth in theepitaxial layer 410 at a distance above the bottom the epitaxial layer410 interfacing with the bottom substrate N+ layer 405. To form such astructure, the trenches 415 in the step shown in FIG. 7B would simply beetched shallower than the substrate.

In addition to the embodiments above, the following strategy may also beimplemented to reduce the Qrr in the body region while achieving a lowon-resistance Rdson. FIG. 9A is a cross sectional view of a high voltageMOSFET (HV-MOSFET) semiconductor power device 500 integrated with aSchottky diode that has an improved diode reverse recovery by minimizingbody charges of this invention while achieving a smaller cell size. Thesmaller cell size increases the cell density, which decreases the onresistance, Rdson. The MOSFET device 500 is supported on an N+semiconductor substrate 505 with an epitaxial layer 510 formed on top ofthe N+ substrate 505. A planar gate 525 is formed on top of a gate oxidelayer 520. A P−body region 530 is formed in the epitaxial layer belowthe gate oxide layer 520 encompassing an N+ source region 535. TheMOSFET device 500 further includes a P+ doped region 540 within theP−body region 530 immediately below the source region 535. A BPSG layer545 covers the gate 525, and has contact openings in it. A source metal550 covers the top surface and the BPSG 545 and fills a contact trench542. The contact trenches 542 extend into the silicon by removing aportion of the source region 535 and P+ dopant region 540. The contacttrenches further extend through an upper portion of the body region 530thus removing a top portion of the body region 530. The source metalfilling in the contact trenches 542 is in direct lateral contact to thesource region 535 and the body contact region 540. A drain metal 560functioning as a drain electrode is formed on the hack side of thesemiconductor substrate 505 thus forming a vertical MOSFET power device.

The MOSFET device may optionally be integrated with a Schottky diode byapplying a Schottky metal as the source metal 550 covering the N+ sourceregion 535, the P+ body contact region 540 and the P−body region 530 andperforming a shallow P-Schottky implant 551 in the exposed parts of theN-Epi layer 510. Furthermore, since a portion of body is removed andfilled with the source metal 550 in the contact trenches, the injectioncharges from the body regions are reduced and a diode reverse recoveryof the HVMOSFET is improved. To further reduce the injection chargesfrom the P−body region 530, the doping concentration of P−body region530 may be reduced. Normally, this reduction in doping concentration ofthe P−body region 530 would alter (reduce) the threshold voltage, Vt, ofthe gate, but this can be countered by increasing the dopingconcentration of P+ region 540. The use of a trench contact helps reducethe cell pitch. Also not much room is needed for a Schottky diode (if aSchottky diode is even used) because the reductions in P body injectioncharges already improve Qrr. Trr, and S. The cell pitch of thisembodiment is greatly reduced, which allows a lower Rdson, while stillachieving the goals of improving the diode reverse recovery.

FIG. 9B is a cross sectional view of an alternate embodiment of aHVMOSFET integrated with a diode similar to the HVMOSFET shown in FIG.9A. The only difference is the HVMOSFET device shown in FIG. 9B has ahigh energy, low dosage boron implant region 555 formed immediatelyunderneath the source metal 550 to improve the body curvature to be notas sharp, which helps keep the breakdown voltage high. This changes theSchottky diode under the source metal 550 into a normal P-N diode.However, the reduction in body region area and dosage improves thereverse recovery characteristics such as Qrr, Trr and S (softness)without the use of a Schottky diode.

FIGS. 10A and 10B are top views showing possible layouts for theembodiments above. FIG. 10A shows a closed cell layout, and FIG. 10Bshows a stripe cell layout. The semiconductor device 500′ of FIG. 9B isused as an example for the layouts in FIGS. 10A and 10B, with the sourcemetal 550, and BPSG 545 removed for clarity. As shown in FIG. 10A, thegate 525 forms a “honeycomb” pattern, with hexagonal openings 1001. TheN+ source regions 535 are located adjacent to the edges of the gate 525and form a ring within the hexagonal opening 1001. The inner edge of thering formed by the source regions 535 is the edge of the contact trench542. The P-type regions 555 and 530 are exposed at the bottom of thecontact trench 542.

FIG. 10B shows a simpler stripe layout. The gate 525 runs in a straightstripe, as does the source region adjacent to it 525. Between the sourceregions 525, the contact trenches 542 follow alongside in a straightstripe. At the bottom of the trench 542, the P-type regions 555, 530 areexposed. The closed cell layout of FIG. 10A may further reduce theamount of P−body regions 530, to achieve even better improvements inQrr, Trr, and S.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is not to be interpreted as limiting. For example, gatedielectric can be to more general term for gate oxide, and a hard masksuch as nitride or deposited oxide may be used instead of field oxide.As another example, though n-channel devices have been illustrated here,the same principles can be applied to p-channel devices simply byreversing the conductivity types of the various layers and regions.Various alterations and modifications will no doubt become apparent tothose skilled in the art after reading the above disclosure.Accordingly, it is intended that the appended claims be interpreted ascovering all alterations and modifications as fall within the truespirit and scope of the invention.

What is claimed is:
 1. A semiconductor power device having a drain electrode disposed in a bottom surface of a semiconductor substrate comprises an active cell area and a termination area, wherein: the semiconductor substrate supports a top epitaxial layer of a first conductivity type having a super-junction structure comprising dopant columns of a second conductivity type extending vertically in said epitaxial layer; a planar gate disposed on top of the epitaxial layer comprising a first planar gate segment and a second planar gate segment separated by a center gap between the first and second planar gate segments; body regions disposed in said top epitaxial layer below outer edges of the first gate segment and the second planar gate segment wherein each of the body regions encompassing a source region of the first conductivity type and each of the body regions extending laterally to a top region of one of the dopant columns; and a Schottky metal layer disposed on top of an insulation layer covering over and completely surrounding the first and second planar gate segments wherein the Schottky metal layer further filling contact trenches opened through the insulation layer at two outer edges of the first and second planar gates and through the center gap between the first and second planar gate segments wherein the contact trenches filled with the Schottky metal layer at two outer edges of the first and second planar gates extending into a top portion of the top epitaxial layer to contact the body regions and the source regions and the Schottky metal filling the trench opened through the center gap between the first and second planar gate segments further extending below the body region and contacting the epitaxial layer.
 2. The semiconductor power device of claim 1 further comprising: a shallow Schottky contact dopant region of the second conductivity type disposed in the epitaxial layer immediately below the Schottky metal layer filling the contact trench opened through the center gap between the first and second planar gate segments.
 3. The semiconductor power device of claim 1 wherein: the epitaxial layer of the first conductivity type is an N-type epitaxial layer having the super-junction structure comprising P-type dopant columns.
 4. The semiconductor power device of claim 1 wherein: said semiconductor power device further comprises a metal oxide semiconductor field effect transistor (MOSFET) power device.
 5. The semiconductor power device of claim 1 wherein: the body regions further comprises a heavy dopant region of the second conductivity type disposed below the source region for laterally contacting the Schottky metal disposed in the contact trenches opened at the two outer edges of the first and second planar gates vertically extending to the top epitaxial layer.
 6. The semiconductor power device of claim 1 wherein: the termination area further comprises field plates electrically connected to floating guard rings formed as dopant regions disposed in the top epitaxial layer.
 7. The semiconductor device of claim 6 wherein: the fielding plates are electrically connected to the floating guard rings through the Schottky metal layer filling the contact trenches vertically opened through the insulation layer extending into the floating guard rings. 